In recent years, an imaging device (hereunder may also be referred to as an “OCT device”) using optical coherence tomography (OCT) making use of coherence of low coherence light has been put into practical use.
The OCT device can obtain a high-resolution tomographic image by irradiating a sample with measuring light and by causing back-scattered light (returning light) from the sample to interfere with reference light. Therefore, a tomographic image of the retina in the fundus of a detection eye is obtained, so that the OCT device is widely used in, for example, ophthalmological examination of the retina.
Here, two types of OCT method are primarily available, that is, time domain-OCT (TD-OCT) and Fourier domain-OCT (FD-OCT). The FD-OCT is a method in which spectrum information is subjected to Fourier transformation, to obtain together pieces of intensity information corresponding to depth-direction positions. Therefore, the FD-OCT can obtain a tomographic image at a higher speed than the TD-OCT in which a coherence gate position is changed for obtaining a depth-direction position.
In OCT measurements in, for example, ophthalmological examination of the retina, a tomographic image may be displaced or may be missing due to eyeball movement (typically, involuntary eye movement). In particular, since it takes time to obtain a tomographic image when a measurement is carried out at a wide angle of view, the probability that the tomographic image is displaced or that the tomographic image is missing is increased.
Accordingly, Japanese Patent No. 2875181 (Patent Document 1) discusses a method that uses a plurality of beams and that narrows a measurement area per one beam to reduce the measurement time. In Patent Document 1, an interferometer that separates nine beams into measuring lights and reference lights is used. The interference lights obtained from the respective beams are dispersed, and the dispersed interference lights are detected with the same two-dimensional sensor array provided for the plurality of beams.
Polarization OCT for carrying out OCT measurement with one spectroscope by obtaining a plurality of interference lights having different polarization states is discussed in “Single Camera Based Spectral Domain Polarization Sensitive Optical Coherence Tomography,” 2007/Vol. 15, No. 3/Optics Express 1054. By this, two interference lights are obtained with one line sensor in one spectroscope so that the size of the device is reduced. The method that uses a plurality of beams and that narrows a measurement area per one beam is not discussed in the document.